Many types of medicine are given as solutions or suspensions of a medical active substance which are subcutaneously or intramuscularly administered.
Many advantages are obtained if the solid medicine, instead of being dissolved or suspended, is formed as small needle shaped pegs which are inserted directly into the tissue where they are dissolved in the tissue fluids and in this way administered in the body. Such pegs can be given a size which is comparable to the size of the needle which is used for the injection of the corresponding fluid medicine. As the medicine itself is the needle, no used needles need to be disposed of after the insertion and consequently the risk of accidental needle scratches is eliminated. Further, most medicine has a longer shelf life in a solid state than in a solution.
A problem with the solid medicament pegs is their size. As they have to be sufficiently thin to be comparable with an injection needle, their thickness is about 1 mm or less. And, to ensure a deposition in the subcutaneous layer of the skin, they have to be short, preferably in the interval 1-10 mm. Such sizes can hardly be handled without a tool such as a pincer and even with a pincer the handling is difficult especially for sight impaired people.
It is an object of the invention to provide means for storage and insertion of solid medicine pegs.
From WO 96/08289 is known a disposable device loaded with one medicine peg which can be inserted into the skin by the device. Whereas such a device is acceptable for the insertion of pegs of a medicament which shall be taken once in a while, it is less convenient for medicaments such as insulin which shall be taken frequently as the user has to bring with him a number of devices corresponding to the number of doses he is going to take during the time he is away from his home. Diabetics will prefer a device by which single pegs can be inserted from a cassette in which a number of such pegs are stored.
WO 96/08289 also describes a device which by pressurized air accelerates the peg from a cassette through a barrel to shoot it into the skin. As it is important for diabetics that the medicament is inserted subcutaneously, a device by which the peg is by a plunger followed to its subcutaneous position is preferred as being more precise than a shooting device.
Further, in the device according to WO 96/08289 no attention has been paid to the fact that the medicament is biodegradable and has to be kept absolutely dry until it is implanted, i.e., the implant has to be stored in a vessel which is diffusion tightly sealed.
Instead of the device in WO 96/08289 by which the user presses the peg through the skin, a device is preferred by which the medicine implant is moved to its subcutaneous position by an impact. Such a device may comprise a socket for a cassette with medicine pegs and a hammer which can, against the force of a spring, be brought to a cocked position from which it can be released to return and hit an anvil from which the impact is transmitted to the medicine peg.
An object of the invention is to provide a cassette loaded with pegs for use in such an insertion device.
A cassette for storing and insertion of solid medicine is according to the invention characterised in that it comprises at least one unit having a first bore accommodating a medicine peg and having a diameter corresponding to the diameter of this peg, a second bore in coaxial extension of the first bore and having a diameter larger than the diameter of the first bore, an inserter comprising an inserter shaft which fits into the first bore and a guiding head connected to the inserter shaft in coaxial extension of this inserter shaft and fitting into the second bore, the inserter shaft having a distal end adjacent to a proximal end of the peg and a proximal end connected to a distal end of the guiding head, which guiding head forms at its proximal end an anvil, the second bore having a length so that the distal end of the inserter shaft is moved to a position extending over the distal end of the housing a distance corresponding to a wanted insertion depth for the when the distal end of the guiding head is moved to the bottom of the second bore.
As the shaft is very thin it is important that the impact force which is transmitted through this shaft is strictly axial as a skew force may cause the shaft to bend. The guiding head sliding through the second bore will compensate a possible skew impact on the anvil end of the guiding head so that only an axial force is transmitted to the shaft. The shaft must only have a length corresponding to the distance which the peg has to be moved to be passed from its position in the first bore to its position in the tissue in which it is inserted. Keeping the shaft as short as possible further minimises the risk for bending.
According to the invention the medicine peg may be moulded in the first bore. This way handling of the small peg is made easier and it is guarantied that the diameter of the peg corresponds to the inner diameter of said first bore.
The head of the inserter may fit into the second bore with a fitting making the head provide a diffusion tight sealing of the proximal end of the second bore, and the distal end of the first bore may be closed by a membrane diffusion tightly sealing the distal end of the unit. This enables a sterile storage of the individual pegs until they are inserted. The membrane is weakened to make it burst in a controlled way not to leave debris of the membrane when the peg is forced through it.
The membrane may be formed integral with the material of the cassette or it may be applied as a separate member, e. g. a metal foil covering the opening of the distal end of the first bore, or it may be embedded in the cassette material adjacent to the distal end of the first bore.
To ease the mounting of an inserter in a unit the transition from the second bore to the first bore may be made funnel shaped.
The guiding head of the inserter may appropriately have a length ensuring that the anvil end of this guiding head projects from the proximal end of the cassette when an impact on the anvil has moved the peg to its wanted position in the skin of a user. As the proximal end of the peg must be placed a distance under the skin, the distal end of the shaft pushing the peg must be moved to a position in which it projects a corresponding distance from the distal end of the unit. The anvil end of the guiding head may be provided with a flange which can be engaged by a draw out mechanism in the not shown insertion device which draw out mechanism can after an insertion of a peg draw the inserter back to hide the distal end of the inserter shaft in the first bore when the peg stored in that bore has been inserted.
The drawing back of the inserter may be accomplished in other ways, e. g. by use of a coil spring surrounding the shaft between the distal end of the guiding head and the bottom of the second bore. Alternatively the compression of the air in the space between the distal end of the guiding head and the bottom of the second bore can be relied on as a means for moving backwards the inserter after it has by an impact on the anvil been moved in a distal direction to insert a peg.
In the cassette the array of units may form a beam, which can be moved by the insertion apparatus so that a new unit is moved to an insertion position each time the hammer mechanism has caused insertion of the peg in the unit which is at the moment placed in the insertion position.
The cassettes may be provided with guiding projections or indentions to ensure their correct guiding through and positioning in the insertion device